1. Field of the Invention
This invention relates in general to the field of electrical wire connections and in particular to methods and apparatus for determining the adequacy of an electrical connection of a coaxial cable to BNC connectors.
2. Description of the Prior Art
A coaxial cable comprises an inner or central conductor surrounded by an insulator which, in turn, is surrounded by a metal shield and finally, an outer layer of insulation surrounding the metal shield. In order to connect one end of a coaxial cable to an end of another coaxial cable, it is required that both the central conductor and the shielding be connected and such that a continuous shield covers the central conductor connection. The finished connection must also include insulation between the central conductor and the shielding.
Because of the complexity of a coaxial cable connection, and for purposes of making certain that a proper and adequate coaxial cable connection is made, special male and female fittings have been created. In the trade, these fittings are known as BNC connectors, or simply a BNC. For example a male fitting is referred to as a male BNC; similarly, a female fitting is referred to as a female BNC. In general, the BNC fittings provide for the ability of a technician to make coaxial cable connections under the difficult conditions usually associated with a connection in the field. In other words, the BNC fittings allow for connections to be made at the physical location were the coaxial cable is being routed with a degree of assurance that a good connection has been made.
Typically, when a coaxial cable connection is to be made, a male BNC is attached to each end of the coaxial cable to be connected. A female BNC is used to join the two male BNCs and make the electrical connection. The male BNCs provide for attaching a pin connector to the central conductor of the coaxial cable, inserting the cable and the pin attached thereto into the male BNC and crimping a sleeve portion of the BNC around the cable. The male BNC further provides for an extension of the shielding around the pin connector in accordance with the design of the male BNC.
The male BNC includes a spring-loaded camming device which allows the male BNC to be connected to the female BNC. A pair of lugs on an extending portion of the female BNC fit within grooves in the spring-loaded device. The spring-loaded device includes a cam surface which is then rotated to firmly lock the lugs to the spring-loaded device by the action of the cam on the lugs. This locks the male BNC to the female BNC. The pin within the male BNC frictionally fits within an opening within a sleeve in the female BNC to make the electrical connection. When the male and female BNCs are locked together, the male pin connector is locking connected to the opening within the female connector. When the male BNC, which is attached to the other end of the coaxial cable, is fitted to and locked with the opposite end of the female BNC, the connection between the central conductors is made. The shielding connection is simultaneously made when the male BNCs are joined to the female BNC interposed therebetween.
A critical aspect of joining two ends of a coaxial cable to each other is the relationship of the pin connector within the male BNC relative to the end of the shielding member within the male BNC so that central conductors are joined and the shielding connection are simultaneously made when the BNCs are locked together. To the extent possible, the design of the male BNC provides for this proper relative relationship but it is subject to the skill of the electrician when attaching the male BNC to the coaxial cable. An experienced electrician will generally properly prepare an end of a coaxial cable and attach a male BNC thereto, such that the combination of his or her skill together with the design of the male BNC will result in the proper relative relationship of the pin connector to the end of the shield within the BNC to achieve an electrically acceptable coaxial cable connection.
Notwithstanding the skill of the electrician and the design of the male BNC, there exists the distinct possibility that the relative position of the pin connector to the end of the shield member within an attached male BNC will not be proper. If the relationship is not proper, a less than satisfactory connection results which usually results in intermittent connections and disconnections. Intermittent connections are the most troubling types of failures. They do not lend themselves to easy detection or isolation. Even extensive field electrical testing might not uncover the problem because at the time of the test, an electrical connection might exist only to later become disconnected, as is the nature of intermittent connections. Then too, such failures might not occur immediately but rather some time later after the entire installation has been completed and the cable is not accessible.
What is needed then are methods and apparatus to allow a simple but effective field test to be performed immediately after a coaxial wire is attached to a male BNC in order to ensure that a proper electrical connection will result when all the BNCs are connected to each other. The present invention accomplishes this highly desirable objective.